1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to an apparatus and a method of removing impurities from a liquid crystal display device.
2. Discussion of the Related Art
In today's information society, a display device is now even more important than ever as a visual information communication medium. A cathode ray tube or braun tube, which is typically as a visual information communication medium, has a problem in that its weight and size are too big. Various kinds of flat display devices have been developed that overcome the limits of the cathode ray tube. The types of flat display devices include a liquid crystal display LCD device, a field emission display FED, a plasma display panel PDP and an electroluminescence EL, and most of them are put to practical use and on the market.
The liquid crystal display device can satisfy the trend of today's electronic products being light, thin, and small. Further, mass productivity of liquid crystal display device has been improved such that they are rapidly be used as a substitute for the cathode ray tube in many application fields. The active matrix liquid crystal display device, which drives a matrix of liquid crystal cells that each use a thin film transistor (hereinafter, referred to as “TFT”), especially has an advantage in that its picture quality is excellent and its power consumption is low. Due to the recent advances in mass production technology, the active matrix liquid crystal display device is now being researched and developed to have a large-size and a high-resolution.
The liquid crystal display device, which displays a picture through such a liquid crystal display panel, controls the light transmissivity of liquid crystal by use of an electric field, thereby displaying a picture. For this, the liquid crystal display device includes a liquid crystal display panel where liquid crystal cells are arranged in a matrix, and a drive circuit to drive the liquid crystal display panel.
FIG. 1 is an expanded perspective view of a related art liquid crystal display panel. As shown in FIG. 1, the related art liquid crystal display panel 1 has a color filter array substrate 20 and a TFT array substrate 30 bonded together. A liquid crystal layer 10 is positioned between the color filter array substrate 20 and the TFT array substrate 30. The liquid crystal display panel 1 shown in FIG. 1 represents a part of the whole effective screen.
In the color array substrate 20, a color filter 24 and a common electrode 26 are formed on the rear surface of an upper glass substrate 22. A polarizer 28 is adhered onto the front surface of the upper glass substrate 22. The color filter 24 has red R, green G and blue B color filter layers arranged therein to transmit light of a specific wavelength range, thereby enabling a color display. A black matrix (not shown) is formed between the color filters 24 of adjacent colors. The black matrix is formed between the red R, green G and blue B color filters 24 to separate the red R, green G and blue B color filters 24 and to absorb the light, which is incident from the adjacent cells, thereby preventing the contrast from being deteriorated.
In the TFT array substrate 30, data lines 34 and gate lines 40 cross each other on the front surface of a lower glass substrate 32. A TFT 38 is formed adjacent to a crossing of the data lines 34 and the gate lines 40. A pixel electrode 36 is formed in a cell area defined between the data lines 34 and the gate lines 40 on the front surface of the lower glass substrate 32.
The TFT 38 includes a gate electrode connected to the gate line 40, a source electrode connected to the data line 34, and a drain electrode facing the source electrode with a channel therebetween. The TFT 38 is connected with the pixel electrode 36 through a contact hole that penetrates the drain electrode. The TFT 38 supplies a data signal from the data line 34 to the pixel electrode 36 in response to a gate signal from the gate line 40. More particularly, the TFT 38 switches a data transmission path between the data line 34 and the pixel electrode 36 in response to a scan signal from the gate line 40, thereby driving the pixel electrode 36. The polarizer 42 is adhered to the rear surface of the TFT array substrate 30.
The pixel electrode 36 is located in the cell area, which is defined between the data lines 34 and the gate lines 40, and is formed of a transparent conductive material having high light transmissivity. The pixel electrode 36 generates a potential difference with respect to the common electrode 26, which is formed at the upper glass substrate 22, as a result of the data signal supplied through the drain electrode. The liquid crystal layer 10 controls the transmissivity of the light, which is incident through the TFT array substrate 30, in response to the electric field applied across the liquid crystal layer 10. If the potential difference between the pixel electrode 36 and the glass substrate 22 is generated, the liquid crystal of the liquid crystal layer 10 that is located between the lower glass substrate 32 and the upper glass substrate 22 rotates by dielectric anisotropy. Accordingly, the light supplied from a light source through the pixel electrode 36 is transmitted to the upper glass substrate 22. The polarizers 28 and 42 adhered onto the color filter array substrate 20 and the TFT array substrate 30 will transmit the polarized light when the polarizing directions of the polarizers perpendicularly cross each other and the liquid crystal of the liquid crystal layer 10 is a 90° TN mode. An alignment film (not shown) is formed at the opposite surfaces the liquid crystal of the color filter array substrate 20 and the TFT array substrate 30.
In order to form an organic insulator and a pattern on the color filter array substrate 20 and the TFT array substrate 30, an organic material or a photo-resist is spread over the upper glass substrate 22 and a lower glass substrate 32 where electrode or line materials are formed. And then, a photo-resist pattern is formed by performing an exposure process in which ultraviolet light is selectively illuminated onto the photo-resist, which is composed of a mask substrate where an area formed of a transparent material and exposed forms an exposure area, and a shielding layer formed on the mask substrate to form a shielding area. Then, a development process is performed in which the exposed photo-resist is developed. Subsequently, the electrode and the line materials are patterned by an etching process using the photo-resist pattern as a mask, thereby forming a pattern. An organic insulating material used as the photo-resist pattern is coated on the glass substrates 22 and 32 by a spinless coating method.
The spinless coating method can achieve a uniform thin film characteristic, regardless of the size of the glass substrates 22 and 32, in comparison with a spin coating method in which a thin film is coated on the substrates 22 and 24 by the rotation of a shaft. When performing the spinless coating method, the glass substrate is placed on a stone surface plate of a coating device. When the coating is completed, the coated substrate is moved to a next process and a new substrate is placed on the stone surface plate. In the process of changing the substrates, impurities, such as an organic material stuck to the nozzle or the particles of the photo-resist, might drop onto the stone surface plate. However, when using the current process of spinless coating, the impurities remain on the stone surface plate. Thus, the stone surface plate is cleaned manually by a person.
FIG. 2 illustrates the effects on a photo-resist or an organic insulating material, when impurities remain on a stone surface plate 100 on which a glass substrate 110 is placed. If the impurities 130 remain on the stone plate 100 when the substrate 110 is placed on the stone surface plate 100, the photo-resist 120 coated on the substrate 22 may develop protrusions from impurities 130 kicked-up during placement of the glass substrate 110. Accordingly, as shown in the cross-sectional diagram of FIG. 2, if the impurities remain on the glass substrate 110, as can be seen from the plan view of FIG. 2, there occurs a phenomenon in that the photo-resist 120 film has a black stain on the right side and a white stain on the left side with the impurities 130 at their center. In this way, impurities remaining on the stone surface plate of the coating device in the related art causes the film thickness of the photo-resist 120 not to be uniform and the stain to be generated in the coated photo-resist 12, thereby decreasing the productivity of the liquid crystal display device and deteriorating the display quality. On the other hand, even though the impurities remaining on the stone surface plate can be removed manually, i.e., by the hand of an operator, it takes a lot of time to perform such a manual operation, thus productivity is reduced.